Geothermal activity, in 2017, supplies some 17-18 percent of New Zealand's electricity. But there are many places in the world that have volcanoes, and many of them are more active than New Zealand's. In New Zealand, geothermal fields cover sleeping volcanoes, not the restless, ready-to-throw rocks volcanoes. Which raises the obvious question of why the islands' sleeping volcanoes can be tapped so effectively.

Finding out answers raises a couple more general questions: what does it take to have a good geothermal energy supply, and is tapping it really as simple as sticking a pipe in the ground?

For New Zealand and other places around the world, the investment in learning how to sustainably use geothermal fields for power has been well worth it. And, with the Paris Agreement to reduce emissions, current geothermal resources seem more likely to be exploited. But carbon emissions have to drop much more steeply than the reductions agreed to in Paris if we're to reach our climate goals. And that means that learning how to use deep geothermal resources is an excellent long-term proposition.